1. Technical Field
The disclosure relates to a network device for supporting a power saving mechanism through an auto-negotiation.
2. Description of the Related Art
When a first application circuit and a second application circuit of a network system are connected to each other through a network medium, the first application circuit and the second application circuit are not always in a data interchange state. For example, during a certain period of time, the first application circuit may continuously receive data from the second application circuit without transmitting any data to the second application circuit, or there may be no data transmitted or received between the first application circuit and the second application circuit. In order to save power in such a data transmission system, when one application circuit does not transmit or receive any data, its corresponding transmitting circuit or receiving circuit should maintain a power saving mode. In more detail, when there is little data transmitted between the first application circuit and the second application circuit, both the first application circuit and the second application circuit could adopt an energy-efficient transmission mode, i.e. a data transmission rate with a lower frequency. The power saving mechanism of the first application circuit and the second application circuit may not be the same, however, making the circuits incompatible, or one of the application circuits may not have any power saving mechanism. For these reasons, when one of the application circuits (e.g. the first application circuit) meets the power saving condition (it is not in the state of receiving data), the first application circuit and the second application circuit cannot set the receiving circuit of the first application circuit to enter a low-power mode based on a predetermined standard procedure.
Moreover, when the receiving circuits of the first application circuit and the second application circuit are both in the low-power mode (a sleep mode, for example), the transmitting circuit of the first application circuit may transmit a trigger signal to the receiving circuit of the second application circuit through the data transmission medium if the transmitting circuit desires to wake up the receiving circuit of the second application circuit from the sleep mode. When the trigger signal reaches the receiving circuit of the second application circuit, however, an echo may rebound, reaching the receiving circuit of the first application circuit such that the receiving circuit of the first application circuit will be erroneously woken up from the sleep mode by the echo. Since the receiving circuit of the first application circuit should maintain the sleep mode continuously, the predetermined standard wake-up procedure of the data transmission system may have errors when the receiving circuit of the first application circuit is erroneously woken up by the echo, and this could influence the flowing data transmission.
In addition, the power saving mechanism of the conventional network systems complies with IEEE 802.3az Energy Efficient Ethernet standard (EEE) defined by the Institute of Electrical and Electronic Engineers (IEEE). The IEEE standard also defines that the power saving mechanism must be implemented in a control circuit through an auto-negotiation (NWAY) defined by IEEE. In other words, in the IEEE standard, a control circuit without the auto-negotiation cannot execute the power saving mechanism as defined by IEEE. Network devices supporting High Definition Multimedia Interface (HDMI) currently fail to support auto-negotiation. Hence, how to support the power saving mechanism defined by IEEE through an auto-negotiation of HDMI, and how to reduce interference caused by echoes have become important issues to be solved in this field.